"Climate change is not just about future scenarios and distant communities. It is here and now, and it is adversely impacting our community's health in more ways than we realize," said study co-author Amir Sapkota. He is a professor of applied environmental health at the University of Maryland's School of Public Health.

In the study, the researchers compared the records of more than 7,000 patients at kidney disease clinics in Boston, New York City and Philadelphia, with extreme heat events in those cities from 2001 to 2012.

Rates of hospitalization and death during the hottest days were consistently higher for black and white patients, but the findings were less clear for Hispanic and Asian patients, the findings showed.

Patients with other health conditions -- such as congestive heart failure, chronic obstructive pulmonary disease and diabetes -- were also at increased risk on the hottest days, the researchers found.

The reasons for this increased risk are unclear, but the investigators noted that one of the body's responses to heat -- lowered blood pressure -- can be a problem for advanced kidney disease patients.

"Hot weather can pose other challenges as well to patients who have to strictly manage fluid intake," said study first author Richard Remigio, a third-year doctoral student at Maryland. "If it's a hot day, we can quench our thirst, but unfortunately they don't have that luxury," he noted.

"We need to ramp up our ability to cope with these increases in extreme heat events. This is our canary in the coal mine," Remigio said in a university news release.

The findings were published online Aug. 9 in JAMA Network Open.

According to Sapkota, "Ongoing climate change is increasing the frequency of extreme heat events. Our results show that these events are particularly harmful to the most vulnerable individuals in our communities."

Community-specific adaptation strategies are needed to protect public health, the researchers concluded.